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Knowledge of the atmospheric turbulence in the telescope line-of-sight iscrucial for wide-field observations assisted by adaptive optics (AO), for whichthe Point Spread Function (PSF) becomes strongly elongated due to theanisoplanatism effect. This one must be modelled accurately to extrapolate thePSF anywhere across the Field of view (FOV) and improve the scienceexploitation. However, anisoplanatism is a function of the Cn2(h) profile, thatis not directly accessible from single conjugate AO telemetry. One may rely onexternal profilers, but recent studies have highlighted more than 10% ofdiscrepancies with AO internal measurements, while we aim better than 1% ofaccuracy for PSF modelling. To tackle this existing limitation, we present theFocal plane profiling (FPP), as a $C_n^2(h)$ profiling method that relies onpost-AO focal plane images. We demonstrate such an approach complies with a1%-level of accuracy on the $C_n^2(h)$ estimation and establish how thisaccuracy varies regarding the calibration stars magnitudes and positions in thefield. We highlight that photometry and astrometry errors due to PSFmis-modelling reaches respectively 1% and 50{\mu}as using FPP on a Keckbaseline, with a preliminary calibration using a star of magnitude H=14 at 20".We also validate this concept using Canadas NRC-Herzberg HENOS testbed imagesin comparing FPP retrieval with alternative $C_n^2(h)$ measurements on HeNOS.The FPP approach allows to profile the $C_n^2(h)$ using the SCAO systems andimprove significantly the PSF characterisation. Such a methodology is alsoELT-size compliant and will be extrapolated to tomographic systems in a nearfuture.

Focal plane $C_n^2(h)$ profiling based on single conjugate adaptive optics compensated images